“It’s a one way transfer. You can send your Miis from your Wii to your 3DS. But, because the Mii Maker on the Nintendo 3DS is a more robust program and has newer features, like hairstyles and eyes and things like that, the Miis you create there can’t go back to the Wii. Beyond that, that’s the only Wii connectivity we’ve talked about.” - NOA Product Marketing Manager Bill Trinen
Just because Nintendo isn’t talking about Wii to 3DS connectivity right now doesn’t mean that it’s not possible with other software. It’ll be interesting to see if the Big N decides to pair the two up down the road.